Cylindrical filters and their manufacture

ABSTRACT

A cylindrical filter is formed from a sheet of filter material which includes two connected layers of filter media. Opposed edges of the sheet are joined to form the cylinder by separating the media adjacent the edges and then sealing together the first of the separated layers followed by sealing the second of the separated layers. The two seals are spaced inwardly of the edges and are spaced from one another. In this way, failure of one seal does not result in failure of the cylindrical filter.

BACKGROUND TO THE INVENTION

1. Field of the Invention

The invention relates to cylindrical filters and their manufacture.

A cylindrical filter is customarily formed from a sheet of filter mediajoined along two opposed edges to form the cylinder. The media may be inthe form of a plain sheet or the sheet may be corrugated, in which casethe joined edges are the final corrugations.

2. Brief Review of the Prior Art

The joint is customarily made by contacting the areas of the sheetadjacent the two edges and then forming a seal between these areas. Ingeneral, the overlap will be with the edges in register, particularlywhere the sheet is pleated. Such a sealed joint is acceptable where thesheet is formed from a single layer of filter media. It is, however,less satisfactory where the sheet is formed from two superimposed layersof media connected together. In this case, the possibility of a flowpath through a single seal is increased.

In EP-Al-0001407 there is disclosed the joining of the edges of a sheetformed of two superimposed layers of media connected together andutilizing a channel strip for connecting the layers of media together.In US-A-3865919 a number of corrugations of a pleated sheet of filtermaterial are bonded together and then provided with a tape or ribbon ofadhesive in a space formed between the corrugations. The adhesive ismelted to form a leak-proof seal.

SUMMARY OF THE INVENTION

According to one aspect of the invention, a pleated cylindrical filterelement comprises a sheet of filter material including at least firstand second layers of filter media. Each of the first and second layersof filter media have first and second edges. A portion of the firstmedia layer near the first edge and a portion of the first filter medialayer near the second edge are sealed by a first seal spaced inwardly ofand extending along the length of the edges. A portion of the secondfilter media layer near the first edge and a portion of the secondfilter media layer near the second edge are sealed by a second sealspaced inwardly of and extending along the length of the edges. Thesecond seal is also spaced from the first seal.

According to a second aspect of the invention, a pleated cylindricalfilter comprises a sheet of filter material including at least first,second, and third layers of filter media. Each layer of filter media hasfirst and second edges. A portion of the first filter media layer nearthe first edge and a portion of the first filter media layer near thesecond edge are sealed by a first seal which is spaced inwardly of andextends along the length of the edges. A portion of the second filtermedia layer near the first edge and a portion of the second filter medialayer near the second edge are sealed by a second seal which is spacedinwardly of and extends along the length of the edges. The second sealis spaced from the first seal. A portion of the third filter media layernear the first edge and a portion of the third filter media layer nearthe second edge are sealed by a third seal which is spaced inwardly ofand extends along the length of the edges. The third seal is spaced fromthe first and second seals.

According to a third aspect of the invention, a pleated cylindricalfilter comprises a sheet of filter material including at least first,second, and third layers of filter media. Each layer of filter media hasfirst and second edges. A portion of the first filter media layer nearthe first edge and a portion of the first filter media layer near thesecond edge are sealed by a first seal which is spaced inwardly of andextends along the length of the edges. Portions of the second and thirdfilter media layers near the first edge of each layer and portions ofthe second and third filter media layer near the second edge of eachlayer are sealed by a second seal which is spaced inwardly of andextends along the length of the edges. The second seal is spaced fromthe first seal.

The following is a more detailed description of some embodiments of theinvention, by way of example, reference being made to the accompanyingdrawings in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of part of a cylindrical pleated filterformed from a sheet of filter material including two connected layers offilter media and joined at the final corrugations,

FIG. 2 is a diagrammatic view of a holder holding the ends of thepleated sheet shown in FIG. 1 before joining and showing a first stagein the joining process,

FIG. 3 is a similar view to FIG. 2, but showing a second stage in thejoining process,

FIG. 4 is a similar view to FIG. 1, but showing a second form of joinbetween the final corrugations,

FIG. 5 is a similar view to FIG. 1 but showing a sheet of filter mediaformed from three connected layers of media and three seals, the sealsconnecting two, four and six layers of media respectively,

FIG. 6 is a similar view to FIG. 4 but showing a sheet of filter mediaformed from three connected layers of media and three seals, each sealconnecting two of the layers,

FIG. 7 is a similar view to FIG. 5 but showing only two seals, one sealconnecting two layers and the other seal connecting all six layers, and

FIG. 8 is a similar view to FIG. 6 but showing only two seals, one sealconnecting two layers and the other seal connecting the remaining fourlayers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring first to FIG. 1, the cylindrical filter is formed from a sheetof filter material having two layers of filter media 10,11 which overlieone another and which are connected to one another. These layers 10,11are covered by upstream and downstream drainage material 12,13. Thelayers of filter media are of nylon.

The sheet is corrugated to form two final corrugations 14,15, which bothextend in the same direction and terminate at respective edges 16,17.

The sheet is formed into a cylinder in the following way.

First, the downstream drainage material 13 is removed from the firstmedia layer 10 inwardly of the edges 16,17 and along the length of theedges 16,17. The first and second media layers 10,11 and the upstreamdrainage material 12 are then separated at the edges 16,17 for thecomplete height of the final corrugations 14,15 and along the completelength of the final corrugations 14,15 to form three separate layers,each of the filter media layers 10,11 having its respective edges 16a,17a, 16b, 17b.

The corrugated sheet with the separated layers is then mounted in theholder shown in FIG. 2. This holder comprises a member 18 of T-shapedcross-section with the head 19 of the T movable so that the edges 20 ofthe head can engage with and disengage from respective supports 21. Thewidth of the head is generally equal to twice the height of thecorrugation of the completed sheet with which it is designed to be used.

The penultimate folds 22 of the sheet, prepared as described above, arearranged around the edges 20 of the head 19 of the member 18 and engagedwith the supports 21. This ensures that the two edges 16,17 areparallel.

The two separated first layers 10 are then brought together by manualmanipulation, as seen in FIG. 2. As shown in FIG. 3, the edges 16a, 17aof the first layer 10 are in register. These layers are then sealedtogether between heated jaws to form a seal extending parallel to theedges 16a,17a and inwardly of the edges. The position and width of thisseal are designated by the letter A in FIG. 1 and it will be seen thatthe seal is adjacent the final folds 23,24 of the pleated sheet.

Referring next to FIG. 3, the second layers are then positioned manuallyto overlie the joined first layers 10 so that the edges 16b,17b of thesecond layer 11 as well as the edges 16a,17a of the first layer 10 areall in register, as shown in FIG. 1. The layers 10,11 are then placedwithin jaws which form a second seal extending inwardly of the edges16,17 parallel to said edges and spaced from the first seal A. This sealconnects together all of the layers. The width and position of this sealare indicated by the letter B in FIG. 1 and it will be seen that thisseal is between the first seal A and the edges 16,17.

Finally, the upstream drainage material 12 is re-assembled over thesecond layers 11.

There is thus formed a pleated cylindrical filter in which the finalcorrugations are joined inwardly of their edges by two parallel butspaced seals A,B. If the seal B should fail in its central portion, theseal A will still remain. If the seal B should fail towards its outeredges, leaking material will still have to pass through the filtermedia. In addition, longitudinal strength is increased and there is anincrease of strength in a cartridge in which the corrugated filter isincorporated.

Six pleated cylindrical filters prepared as described above withreference to the drawings were tested in the following way.

All six cartridges were placed in an autoclave at 140° C. for fourperiods of one hour each. All six cartridges were tested for forwardflow before the four one hour cycles and after the four one hour cycles.The filters were tested water wet at 2.61 kPa (18 psi).

An acceptable production limit for such forward flow is 10 ml/min and anacceptable limit in use is 22 ml/min.

The results were as follows:

    ______________________________________                                        FORWARD FLOW IN MLS/MIN                                                       Filter No   Before Steaming                                                                            After Steaming                                       ______________________________________                                        1           1.97         1.30                                                 2           2.05         1.60                                                 3           2.13         1.00                                                 4           2.07         1.38                                                 5           2.17         1.18                                                 6           1.93         1.25                                                 ______________________________________                                    

It will thus be seen that all filters remain well within the acceptablelimits after autoclaving. This indicates that there has been no failureof the seals.

It will be appreciated that the method of manufacture and constructiondescribed above need not be applied to pleated filters, it could beapplied to filters in which no pleats are provided. Further, the joinmay not be with the two edges in register, it could be with the twoedges overlapping.

A second form of join is shown in FIG. 4. Aspects of this join and thejoin described above with reference to FIGS. 1 to 3 are the same andthese aspects will not be described in detail.

In this second form of join, the first seal A is formed as describedabove with reference to FIGS. 1 to 3. However, after formation of thisseal A, the portions of the first media layer 10 between the seal A andthe edges 16b,17b of the second media layer 11 are cut-away. As shown inFIG. 4, the edges 16a, 17a of the first layer 10 are in register and arespaced from the edges 16b,17b of the second layer 11, which are also inregister.

Thus, when the second media layers 11 are positioned as shown in FIG. 3,these layers 11 only partially overlie the first media layers 10 andportions of the second media layers 11 are in contact. The second seal Bis formed between these contacting second media layer portions 11, asshown in FIG. 4.

The upstream drainage material 12 is then re-assembled.

It will be appreciated that filters having three or more media layersmay be joined by either of the methods described above with reference tothe drawings. In such cases, the media layers may all be separated andjoined successively in pairs by spaced seals, so that there are as manyseals as layers. This is shown in FIGS. 5 and 6 where parts common toFIGS. 1 and 4 and to FIGS. 5 and 6 will be given the same referencenumerals and will not be described in detail. In these embodiments, thecylindrical filter is formed from a sheet of filter material havingthree layers of filter media 10,11,25 which overlie one another and areconnected to one another. The layers of filter media 10,11,25 are ofnylon.

The sheet is corrugated to form two final corrugations 14,15, which bothextend in the same direction and terminate at respective edges 16,17.

The sheet of FIG. 5 is formed into a cylinder in the way described abovewith reference to FIG. 1 except that the third media layer 25 is alsoseparated at the edges 16,17 for the complete height of the finalcorrugations 14,15 and along the complete length of the finalcorrugations 14,15 to form six separate layers.

The layers 10,11 are joined as described above with reference to thedrawings. The two portions of the separated third layer 25 are thenbrought together by manual manipulation. As shown in FIG. 5, both edges16a, 17a, 16b, 17b, 16c, 17c of all of the filter media layers 10, 11,25 are in register. The layers are then sealed together between heatedjaws to form a seal extending parallel to the edges 16,17 and inwardlyof the edges. The position and width of this seal are designated by theletter C in FIG. 5 and it will be seen that the seal is adjacent thefinal folds, and closer to the edges 16,17 than the previously formedseals A,B.

Finally, the upstream drainage material 12 is re-assembled over thesecond layers 11.

There is thus formed a pleated cylindrical filter in which the finalcorrugations are joined inwardly of their edges by three parallel butspaced seals A,B,C. If the seal C should fail in its central portion,the seals A and B will still remain. If the seal C should fail towardsits outer edges, leaking material will still have to pass through thefilter media. In addition, longitudinal strength is increased and thereis an increase of strength in a cartridge in which the corrugated filteris incorporated.

The second form of join is shown in FIG. 6. Aspects of this join and thejoin described above with reference to FIGS. 1 to 5 are the same andthese aspects will not be described in detail.

In this second form of join, the first seal A and the second seal B areformed as described above with reference to FIG. 4. However, afterformation of the second seal B, the portions of the second media layer11 between the seal B and the edges 16c,17c of the third media layer 25are cut-away. As shown in FIG. 6, the edges 16b,17b of the second layer11 are in register and are spaced from the edges 16c,17c of the thirdlayer 25, which are also in register.

Thus, when the portions of the third media layer 25 are positioned asshown in FIG. 6, these portions only partially overlie the first andsecond media layers 10,11 and are in contact. The third seal C is formedbetween these contacting third media layer portions 25, as shown in FIG.6.

Alternatively, two layers (or more where there are four or more layers)near each edge may be joined together so that there are less seals thanlayers. This is shown in FIGS. 7 and 8 where parts common to FIGS. 1 to6 and to FIGS. 7 and 8 will be given the same reference numerals andwill not be described in detail.

In FIG. 7, the third media layer 25 is not separated from the secondmedia layer 11 and the portions near the edges 16b,17b,16c,17c of thesetwo layers 11,25 are sealed together as one, as described above withreference to FIGS. 2 and 3. There are thus only two seals A,B, with thesame seal A connecting two portions of the first media layer 10, and theother seal B connecting all six portions of all of the media layers10,11,25.

In FIG. 8, the third media layer 25 is not separated from the secondmedia layer 11 and the portions near the edges 16b,17b,16c,17c of thesetwo layers are sealed together as one, as described above with referenceto FIG. 4. There are only two seals A,B with the inner seal connectingthe two inner media layers 10, and the outer seal connecting the fourportions of the remaining media layers 11,25.

What is claimed is:
 1. A pleated cylindrical filter comprising a sheetof filter material including at least first and second layers of filtermedia, each having first and second edges, wherein a portion of thefirst layer near the first edge and a portion of the first layer nearthe second edge are sealed by a first seal spaced inwardly of andextending along the length of the edges, and a portion of the secondlayer near the first edge and a portion of the second layer near thesecond edge are sealed by a second seal spaced inwardly of and extendingalong the length of the edges and spaced from the first, whereby thesheet of the filter material is formed into a cylinder.
 2. A pleatedcylindrical filter according to claim 1 wherein the first and secondedges of each layer are in register and a portion of the first layernear the first edge is sealed to a portion of the first layer near thesecond edge by said first seal and the portions of the second layer nearthe first and second edges are sealed by the second seal.
 3. A pleatedcylindrical filter according to claim 2 wherein the registered edges ofthe first layer are spaced from the registered edges of the second layerso that the portions of the second layer are in contact, the second sealbeing between said contacting portions.
 4. A pleated cylindrical filteraccording to claim 2 wherein the edges of the second layer are inregister with the edges of the first layer so that the second seal sealstogether the first and second layers.
 5. A pleated cylindrical filteraccording to claim 2 wherein the second seal is positioned between thefirst seal and the registered edges of the second layer.
 6. A pleatedcylindrical filter according to claim 2 wherein the sheet of filtermaterial is corrugated with the seals being formed between finalcorrugations of the sheet.
 7. A pleated cylindrical filter according toclaim 6 wherein the first seal is adjacent the final folds.
 8. A pleatedcylindrical filter according to claim 2 wherein the first layer isdownstream from the second layer.
 9. A pleated cylindrical filteraccording to claim 2 wherein the sheet of filter material includes alayer of surface drainage material on both surfaces thereof.
 10. Apleated cylindrical filter according to claim 9 wherein the layers ofsurface drainage material are not sealed to the layers of filter media.11. A pleated cylindrical filter according to claim 1 wherein the layersof filter media include nylon.
 12. A pleated cylindrical filtercomprising a sheet of filter material including, at least first, secondand third layers of filter media, each having first and second edges;wherein a portion of the first layer near the first edge and a portionof the first layer near the second edge are sealed by a first seal whichis spaced inwardly of and extends along the length of the edges; whereina portion of the a second layer near the first edge and a portion of thesecond layer near the second edge are sealed by a second seal which isspaced inwardly of and extends along the length of the edges and isspaced from said first seal; and wherein a portion of the third layernear the first edge and a portion of the third layer near the secondedge are sealed by a third seal which is spaced inwardly of and extendsalong the length of the edges and is spaced from the first and secondseals, whereby the sheet of filter material is formed in a cylinder. 13.A pleated cylindrical filter according to claim 12 wherein the edges ofthe first layer, the edges of the second layer and the edges of thethird layer are in register so that the second seal seals together thefirst and second layers and the third seal seals together the first,second and third layers.
 14. A pleated cylindrical filter according toclaim 12 wherein the edges of the first layer are spaced from the edgesof the second layer so that the portions of the second layer are incontact, said second seal contacting portions of the second layer andwherein the edges of the second layer are spaced from the edges of thethird layer so that the portions of the third layer are in contact, saidthird seal sealing the contacting portions of the third layer.
 15. Apleated cylindrical filter comprising a sheet of filter materialincluding at least first, second and third layers of filter media, eachhaving first and second edges; wherein a portion of the first layer nearthe first edge and a portion of the first layer near the second edge aresealed by a first seal which is spaced inwardly of and extends along thelength of the edges, wherein portions of the second layer and thirdlayer near the first edge of each layer and portions of the second layerand third layer near the second edge of each layer are sealed by asecond seal which is spaced inwardly of and extends along the length ofthe edges and is spaced from the first seal, whereby the sheet of filtermaterial is formed in a cylinder.
 16. A pleated cylindrical filteraccording to claim 15 wherein the second seal is positioned between saidfirst seal and the edges of the second and third layers.
 17. A pleatedcylindrical filter according to claim 15 wherein the edges of the firstlayer, the edges of the second layer and the edges of the third layerare in register so that the second seal seals together the first, secondand third layers.
 18. A pleated cylindrical filter according to claim 15wherein the edges of the first layer are spaced from the edges of thesecond and third layers so that the portions of the second layers, thesecond seal sealing the contacting portions of the second layers andsealing together the second and the third layers.